As in previous growing seasons, the use of Bt hybrids will remain a key tactic in 2013 for corn rootworm protection. However, the number of producers using soil insecticides is increasing.

Mike Gray, a University of Illinois professor of agricultural entomology in the Crop Sciences Department, polled producers at the 2013 Corn and Soybean Classics (producer meetings in Illinois) to find out if they intended to plant a Bt hybrid for corn rootworm protection in 2013.

“On average, for the five locations, nearly 92 percent of the producers indicated that Bt hybrids would be targeted at corn rootworms for the upcoming growing season,” Gray reported. He thinks that the results indicate, as more pyramided Bt hybrids enter the marketplace, there will be significant changes in the choice of refuge.

“In 2012, the traditional 20 percent structured refuge was still the dominant approach used by producers in the Corn Belt. Based upon responses received at the 2013 Corn and Soybean Classics, this refuge strategy will no longer remain dominant for Illinois producers,” he said.

He thinks that most producers who took part in the regional meetings will choose the 5 percent seed blend (refuge-in-a-bag, or RIB). Slightly more than 40 percent indicated that they will be moving in this new direction.

The second most common refuge tactic will be the 10 percent seed blend (RIB), with just under one third relying upon this approach. Together, these data indicate that nearly three out of four producers who responded to this question will use a seed blend as their corn rootworm refuge management strategy.

“The advantages of an RIB are straightforward—convenience, ensured compliance, and, based upon emergence patterns and inter-field dispersal dynamics of adults for effective resistance management of western corn rootworms,” Gray said.

Gray also said that in 2013, he anticipates a sharp increase in the use of planting-time soil insecticides with corn rootworm Bt hybrids. On average, nearly half the producers indicated they intend to use both a soil applied (at-planting) insecticide with their corn rootworm Bthybrid this spring.

“From my perspective, the escalation of soil insecticide use along with corn rootworm Bthybrids has been fueled primarily by concerns about Bt resistance and high commodity prices,” he said.

Producers who intend to use a soil insecticide with their corn rootworm Bt hybrid this spring offered several reasons for this approach, with concerns over secondary insect infestations and Bt resistance as the top issues cited. However, more than a quarter of the producers acknowledged that they view the use of a soil insecticide with a corn rootworm Bt hybrid as “cheap insurance.”

Gray said that more research is needed on the potential insect resistance management benefits of a soil insecticide used in combination with a Bt hybrid.

“I think it is worth mentioning that one of the key benefits touted concerning the use of Bthybrids for corn rootworm management was the reduction of soil insecticide use,” he said. “It is a bit surprising that 10 years after the first Bt hybrids entered the marketplace for corn rootworms in 2003 that a heightened interest in the use of soil insecticides has surfaced in such a significant fashion.”

Gray concluded that, unlike the record-breaking warm temperatures of March 2012 that caused early emergence of western corn rootworm, this year’s weather does not favor early emergence.